This invention relates to coating compositions. More particularly, the invention relates to the use of polyester resins in coating compositions, said compositions being capable of conventional application using a low level of organic solvent and capable of curing at a low temperature.
There have been recent concerns as to the polluting effects and health concerns associated with the use of organic solvents. Many coating compositions contain appreciable amounts of organic solvents. Precautions in the use of the coating compositions and the installation of solvent recovery systems have alleviated some of the concerns. However, it would still be desirable to formulate coating compositions containing little or no organic solvent.
Many attempts have been made to lower the organic solvent content of various coating compositions. One line of work has used water as the liquid carrier in place of the organic solvent. However, this has necessitated changes in the resin formulations with a consequent change in performance obtained from the coating compositions. Another line of work has attempted to formulate coating compositions containing a high solids content and thus low organic solvent content. The problem associated with many of the high solids coating compositions has been the fact such compositions normally are highly viscous and are difficult to apply using conventional coating techniques. The formulation of a coating composition having a low organic solvent content which also possesses a viscosity which allows the composition to be applied by conventional coating techniques would be most desirable.
Still another concern with prior used organic solvent containing coating compositions has been the energy demands needed to drive off the solvent and cure the resultant film. Besides the aforediscussed possible pollution concerns with organic solvents there is also the desire to use less energy in order to remove the solvent and form a durable film from coated substrates. Thus, a coating composition which can be applied by conventional means to a substrate and use a small amount of energy to remove solvent and cure the coating would be most desirable.
There have now been found polyester resins which when properly formulated into coating compositions provide compositions which can be readily applied and cured with a low energy demand to give coatings having a desired set of properties.
As used herein all percents and ratios are by weight unless otherwise indicated.